Revert "Use iOS 13 dark content status bar style (flutter#13119)"

This reverts commit fdba8f6.

Author: NoamDev

shell/platform/darwin/ios/framework/Source/FlutterPlatformPlugin.mm

@@ -166,22 +166,17 @@ - (void)restoreSystemChromeSystemUIOverlays {
 }
 
 - (void)setSystemChromeSystemUIOverlayStyle:(NSDictionary*)message {
-  NSString* brightness = message[@"statusBarBrightness"];
-  if (brightness == (id)[NSNull null])
+  NSString* style = message[@"statusBarBrightness"];
+  if (style == (id)[NSNull null])
     return;
 
   UIStatusBarStyle statusBarStyle;
-  if ([brightness isEqualToString:@"Brightness.dark"]) {
+  if ([style isEqualToString:@"Brightness.dark"])
     statusBarStyle = UIStatusBarStyleLightContent;
-  } else if ([brightness isEqualToString:@"Brightness.light"]) {
-    if (@available(iOS 13, *)) {
-      statusBarStyle = UIStatusBarStyleDarkContent;
-    } else {
-      statusBarStyle = UIStatusBarStyleDefault;
-    }
-  } else {
+  else if ([style isEqualToString:@"Brightness.light"])
+    statusBarStyle = UIStatusBarStyleDefault;
+  else
     return;
-  }
 
   NSNumber* infoValue = [[NSBundle mainBundle]
       objectForInfoDictionaryKey:@"UIViewControllerBasedStatusBarAppearance"];